Sewage lift station gas trap

ABSTRACT

A sewage lift station including a variable volume breathing assembly which normally isolates the interior of the sewage tank from the surrounding atmosphere and thereby eliminates the escape of offensive gas. The assembly traps the sewer gas in the tank as the effluent level rises and falls between predetermined limits and effects relatively innocuous venting of a portion of the sewer gas from the tank to the atmosphere should an excessive amount accumulate over a period of time or should an abnormal rise in the effluent level occur resulting in a rise in the pressure of the trapped gas exceeding ambient atmospheric pressure.

United States Patent [191 Wilson 1 SEWAGE LIFTYSTATION GAS TRAP [76] Inventor: Rona] E. Wilson, 1100 E. Side Dr.,

Bossier City, La. 71010 [22] Filed: Nov. 15, 1968 [21] Appl. No.: 776,162

[52] US. Cl. .[417/40, 138/30 [51] Int. Cl. F04b 49/00 [58] Field of Search 220/44, 44 A, 85 B; 417/36, 40, 118; 4/43, 219; 210/538, 539; 137/587 [56] References Cited UNlTED STATES PATENTS 2,342,355 2/1944 Mercier 220/85 3,123,249 3/1964 Gorand et al..... 137/587 3,260,371 7/1966 Wall 210/533 753,174 2/1904 Smith 4/43 1,762,419 6/1930 Pettis 1 4/219 3,318,248 5/1967 Rembold.... 417/40 1,690,072 10/1928 Johnson 220/85 B 2,643,602 6/1953 Martin 220/85 B X [451 Apr. 30, 1974 Attorney, Agent, or FirmStrauch, Nolan, Neale, Nies & Kurz [57] ABSTRACT A sewage lift station including a variable volume breathing assembly which normally isolates the interior of the sewage tank from the surrounding atmosphere and thereby eliminates the escape of offensive gas. The assembly traps the sewer gas in the tank as the effluent level rises and falls between predetermined limits and effects relatively innocuous venting of a portion of the sewer gas from the tank to the atmosphere should an excessive amount accumulate over a period of time or should an abnormal rise in the effluent level occur resulting in a rise in the pressure of the trapped gas exceeding ambient atmospheric pressure.

14 Claims, 5 Drawing Figures 2 AK 9 .A

SEWAGE LIFT STATION GAS TRAP BACKGROUND OF THE INVENTION This invention relates generally to sewage lift stations and more particularly to a novel sewage lift station which substantially eliminates the escape of offensive gases from the lift station tank to the surrounding atmosphere while permitting relatively innocuous venting of a portion of the gases from the tank to the atmosphere in event of excessive accumulations of gases or an abnormal rise in the effluent level.

Sanitary sewage systems generally require a slope whereby sewage flows by gravity to a suitable treatment plant or other disposal system. In areas where the ground surface is substantially flat and the sewer line may be a few miles long it becomes impractical and uneconomical to bury the discharge end of the line sufficiently deep to maintain the required slope.

Sewage lift stations have been found useful in raising the sewage to a higher level where it may be discharged into the entrance of another sewer line at the higher level. Thus, in a system where sewage is to be transferred over a relatively long distance to a treatment station, several lift stations may be employed to periodically raise the sewage from a lower to a higher level and thereby render it feasible to maintain the required slope to ensure gravity flow.

Various types of sewage lift stations are known, such as that illustrated by US. Pat. No. 3,337,455, of which I am a co-inventor. These generally have included a covered concrete tank buried sufficiently deep in the ground to receive effluent from the discharge end of a gravity flow sewer line and of sufficientheight to dispose the tank cover or top at or slightly above ground level. When the effluent level in the tank reaches a predetermined high level, a float controlled switch assembly automatically energizes a pump which lifts the effluent from the tank to a higher level where it is deposited in another gravity flow sewer line. The pump is automatically de-energized when the effluent level in the tank drops to a predetermined low level, the level then being allowed to rise until the pump is again automatically energized.

Various problems are associated with the normal operation of known lift stations. In conventional systems in which sewer gases which collect above the liquid effluent in the lift station tank are continuously vented to atmosphere without treatment, offensive odors emanating from the effluent in the tank and the escaping gases permeate the surrounding atmosphere. Additionally, certain of these gases are known to be poisonous and inflammable and, for this reason, systems such as that described in my prior patent have been proposed to treat these gases at substantial expense to render them innocuous before they are vented to the atmosphere. These systems, although quite successful in operation, require the use of rather sophisticated treatment equipment which is quite costly and, therefore, economically undesirable.

As mentioned in my prior patent, the gases in the tank generally include carbon dioxide, methane, and hydrogen sulfide, in varying volumes and percentages in the mixture. The methane which is odorous, inflammable and lightest in weight tends to collect near the top of the tank, while the hydrogen sulfide (H 8) which is odorous, poisonous, inflammable and heaviest in weight tends to collect in the lower portion of the tank adjacent the surface of the liquid effluent. The carbon dioxide, which is generally in weak concentrations, is odorless and harmless.

Thus, it is apparent that these gases should not simply be continuously vented to the atmosphere without treatment because of their odorous and possible harm- SUMMARY OF THE INVENTION Accordingly, the primary object of this invention resides in the provision of a novel sewage lift station of relatively simple, low cost construction which eliminates odor from the surrounding atmosphere by normally trapping the sewer gases within the tank and effects relatively innocuous increments of the gases to vent periodically to the atmosphere when an excessive amount accumulates or when an occasional abnormal rise in the level of the effluent in the tank occurs, for example, due to entry into the system of quantities of storm sewage during rain storms and as a result of melting snow and ice.

A related object resides in the provision of a novel sewage lift station comprising an enclosed tank provided with a flexible, variable volume breathing assembly which normally isolates the interior of the tank from the surrounding atmosphere and maintains the gases trapped above the effluent at substantially atmospheric pressure as the level of the effluent within the tank rises and falls between predetermined upper and lower limits. Additionally, the breathing assembly permits a small, relatively innocuous increment of the trapped gases to vent to the atmosphere when an-excessive amount accumulates or when the effluent level exceeds the predetermined upper limit.

BRIEF DESCRIPTION OF DRAWING Other objects and advantages willlbecome apparent from reading the following description and appended claims when read in conjunction with the appended drawings wherein:

FIG. 1 is a vertical section view of a preferred embodiment of the novel sewage lift station according to the invention;

FIG. 2 is an enlarged fragmentary sectional view of the novel breathing assembly incorporated into the lift station of FIG. 1;

FIG. 3 is a vertical section view of a second embodiment of the invention in which the sewage tank is buried underground and the breathing assembly is mounted externally of the tank; and

FIG. 4 is a vertical section view of a third'embodiment of the invention in which the breathing assembly is mounted externally of the tank due to the presence of operational equipment within the tank.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS Referring now the preferred embodiments of the invention illustrated in FIGS. 1 and 2, the sewage lift sta tion comprises sewage tank 10 having side walls 12,

bottom wall 16, and top wall 18, which is provided with opening normally sealingly closed by removable cover 22, and circular vent opening 21 which receives breathing assembly 40 hereinafter described in detail. The top surface 19 of wall 18 is usually flush with or extends slightly above ground level 24.

Effluent 25 flows into tank 10 from the discharge end of a gravity flow sewer line (not shown) through conduit 26 passing through right wall 12 and discharging and having its outlet 27 located below the lower predetermined effluent level in the tank. Similarly, effluent is pumped from tank 10 through outlet conduit 28 passing through wall 12 and upwardly through lift pipe 29 by a suitable pump -29(a)- which is controlled automatically by a conventional float control switch assembly -29(b)-. The normal operation is such that when the effluent level in tank 10 rises to an upper predetermined level indicated by dotted line 30 a float (not shown) energizes the pump to remove effluent from the tank through conduit 28 and pipe 29 and delivers it to another gravity flow sewer line connected to lift pipe 29 at a higher level. When the level of the effluent in the tank drops to a lower predetermined level indicated by dotted line 32, the pump is stopped and the effluent level therein is again permitted to rise to upper level 30.

lt is desirable that the interior of the tank 10 be isolated from the atmosphere to prevent offensive odors emanating from the effluent 25 and the harmful gases which collect in space 34 above the effluent from en- .tering and permeating the surrounding atmosphere.

However, it is also desirable to maintain the space 34 at atmospheric pressure as the effluent level rises and falls between the predetermined levels to prevent any pressure build-up which may cause structural damage to the sewage system and adversely affect gravity flow of the effluent to the treatment or disposal location.

According to this invention, a variable volume breathing assembly functioning normally to seal the interior of the tank from the atmosphere and to maintain the pressure in space 34 at substantially atmospheric pressure is provided. Assembly 40 also functions to effect relatively innocuous increments of the gases in space 34 to vent to the atmosphere when an excess thereof accumulates in tank 10 over a period of time or when an abnormal rise in the effluent level above level 30 occurs.

Referring particularly to FIG. 2, breathing assembly 40 comprises a fitting 42 including a tubular pipe section 43, an upper annular flange section 44 welded to pipe section 43, and a sealing O-ring 46, preferably seated in a ring groove 47 in surface 19, on which flange 44 normally rests. Pipe 43 has an outer diameter smaller than that of the wall defining opening 21 to provide annular vent passage 50 therebetween and preferably mounts angularly spaced centering pins on its periphery to assure general centering of fitting 42 with respect to opening 21.

A flexible bag 52 is suspended from fitting 42 within space 34 by a tubular mouth portion 53 fitted around the lower end of pipe section 43 and retained thereon by a circular band clamp 54. The bag also has an opening 56 defined by tubular extension 58, the end of which is normally retained closed by a surrounding spring 60. Extension 58 and spring 60 function as a one-way flapper valve 61 in that they will permit the escape of excessively high pressure air from the inside of bag 52 to space 34, but will not permit gas flow therethrough in the reverse direction.

Bag 52 is preferably constructed of plastic, rubber, or like material so as not to be affected adversely by the gases within space 34, particularly the hydrogen sulfide.

Breathing assembly 40 operates in the following manner, with the normal sealing position of assembly 42 being that shown in the drawing. Bag 52 is partially collapsed since the effluent level is above lower limit 32 and flange 44 rests on O-ring 46 which engages the upper surface 19 of wall 18, thereby forming a seal around opening 21 to prevent the escape of odors and gases from tank 10 through annular passage 50. Flange 44 is normally maintained in sealing engagement with O-ring 46 by the weight of fitting 42 and bag 52 suspended therefrom. The interior of bag 52 is, of course, subjected to atmospheric pressure through the bore of pipe 43.

As the level of effluent 25 rises in tank 10 toward the upper level limit 30 at which point the pump is energized to remove effluent 25 from tank 10, the gases in space 34 will be displaced by the rising effluent with consequent increasing of the effective pressure thereof. This effective increased pressure acting on the outer surface of bag 52 compresses the bag forcing air into the atmosphere until the internal and external pressures acting on the bag are again balanced at atmospheric pressure or until the bag is fully collapsed by reason of the level reaching the upper limit level 30 without lifting flange 44 off the O-ring seal 46. As a consequence,no gases are vented through passage 50 until after the bag is fully collapsed. Any further rising of the effluent level increases the gas pressure in chamber 34 above the opposing atmospheric pressure until the effective pressure in chamber 34 acting on the undersurfaces of assembly 40 overcomes the opposing force of the atmospheric pressure acting on assembly 40 to lift flange 44 off of seal ring 46 to vent gases through passage 50 to the atmosphere until the opposing atmospheric pressure reseats flange 44 on seal ring 46 sufficiently to seal off the vent passage.

Similarly, when the sewage level falls in tank 10 toward the lower level limit 32, the gases in space 34 will tend to expand and decrease in pressure and thereby create a vacuum in the tank. Bag 52 being open to the atmosphere will be inflated under influence of the opposing atmospheric air and expanded untilthe opposing pressures acting thereon are again balanced at atmospheric pressure.

The size of the bag 52 to be employed will depend upon the volume of space 34 between the predetermined upper and lower limits 30 and 32 of the effluent. For example, assuming tank 10 is square, the cross sectional area across the surface of effluent 25 is sq. ft., and thevertical fluctuation of the effluent level between limits 30 and 32 is 3 ft., the change in volume of .space 34 for each fluctuation would be 300 cu. ft.

ternally and externally thereon balanced at atmospheric pressure.

Under normal circumstances, when the effluent level reaches the upper limit 30, bag 52 will be fully collapsed to compensate for the gas displaced in tank due to the rising effluent level.

Additionally, during each period of time required for the effluent to rise from level 32 to level 30, there will be a very small amount of excess gas produced in tank 10 by bacterial action occurring within the effluent 25. This excess volume of gas will cause an increase in pressure which cannot be compensated for by the already fully collapsed bag 52. Therefore, the increased pressure, acting on flange 44 through passage 50, will overcome the weight of fitting 42 and bag 52 to lift flange 44 off of ring 46 and thereby permit the small amount of excess gas to vent from tank l0.to atmosphere around O-ring 46.

The increase in pressure in tank 10 above atmospheric required to lift assembly 40 depends on the weight of the assembly and on the flange area circumscribed by O-ring 46. For example, if assembly 40 weighs 30 pounds and the diameter of O-ring 46 is 18 inches, thereby circumscribing an area of 254 sq. inches, the pressure increase which would be required to lift the assembly and permit the escape of excess gas through passage 50 and around O-ring 46 would be approximately 0.l2 pounds per square inch. The small portion of gas which is permitted to escape under these conditions is relatively innocuous and harmless, since the amount of gas produced through the mitosis of the bacteria is minute compared to the amount of gas displaced by the fluctuation in the effluent level between limits 32 and 30, and is rapidly intermixed and diluted in the gas mixture present in space 34.

During heavy rain periods, breathing assembly 40 will similarly function to permit gases to escape from tank 10 when the sewer lines are heavily infiltrated by large amounts of rain water. During such periods, the effluent level in tank 10 may rise well above limit 30, e.g., up to level 62, because in most instances, the pumps which remove effluent from the tank through conduit 28 are not of sufficient capacity to keep up v with the constant inflow through conduit 26.

The odor problem during these periods is not critical because the effluent is extremely diluted by the large amounts of rain water, thus the gases permitted to escape are relatively innocuous.

After the heavy rain periods, the pumps begin to lower the effluent level in tank 10 from level 62 down to lower limit 32. When the effluent 25 is at level 62, the space 34 above the effluent will be at atmospheric pressure and bag 52 will be fully collapsed. As the effluent level begins to fall, a vacuum will be created in the tank and the bag will expand to its maximum volume, fully inflated condition. However, since the maximum volume of the bag, which corresponds to the volume of the tank between limits 30 and 32, is less than the volume between levels 62 and 32, an excess pressure inside the bag, or stated another way, an excess vacuum outside the bag in tank 10 will be created as the effluent level continues to drop toward lower level 32. Because this pressure differential between the inside and outside of the bag could cause a rupture of the bag, tubular extension 58 and spring 60 are provided and function as a one-way flapper valve 61 which permits the high pressure air inside the bag to escape into the vacuum space in tank 10 until the inside and outside pressures are equalized. In actual practice, the closing tension on spring 60 would be adjusted so that the flapper valve would open when a small pressure differential, e.g., about two ounces, existed between the inside and outside of the bag, thus preventing any undue tension on the bag itself. 1

When the effluent level reaches height 32, the pumps will be deenergized, the flapper valve 61 closed, and the breathing assembly 40 will return to normal operation as previously described.

It should be noted that the outlet 27 from feed conduit 26 is positioned below lower limit 32 and, thereby, always discharges the incoming sewage below the surface level of effluent 25 in the tank. This is significant because the gravity sewer line to which conduit 26 is connected is not, as a rule, flowing completely full. Thus, if the outlet of conduit 26 were not positioned as shown, instances might occur in which breathing of the bag could cause a pressure loss back through the infeed sewer line. This would result in breathing in and out of manholes upstream in the sewer line and cause some odor problems around these manholes. However, by positioning the outlet 27 of conduit 26 below the lower level of affluent 25, these odor problems are avoided.

In actual practice, there may be some instances in which it is not feasible to utilize the embodiment of FIG. 1 which mounts the flexible bag of the breathing assembly within the sewage tank. Two such instances are illustrated in the embodiments of FIGS. 3 and 4.

The embodiment of FIG. 3 may be used when the enclosed sewage tank must be completely buried beneath the ground level 72. Sewage effluent flows into tank 70 through inlet conduit 74 and is pumped from the tank by way of outlet conduit 76 in the same manner as described with respect to FIG. 1, with the effluent level in the tank normally fluctuating between lower and upper limits 78 and 80, respectively.

A tubular shaft or conduit 82 is connected to and extends upwardly from tank opening 84 to ground level 72 or slightly thereabove. A cover 86 is provided for shaft 82 and has connectedly extending therethrough tubular pipe sections 88 and 90 to which the breathing assembly including bag 92 and valve 94 are respectively connected. The flexible breathing bag 92, constructed identically to bag 52 of FIG. 1 except that it doesnt have a flapper valve integral therewith, is retained on pipe 88 by band clamp 93 and is expanded and contracted as the effluent level in tank 70 respectively rises and falls between the predetermined limits 78 and 80.

Connected to the outer end of pipe 90 is a suitable conventional pressure and vacuum relief valve 94, schematically illustrated in FIG. 5, which may comprise a tubular section 96 having end plates 98 and 100 defining a chamber 101, the plates 98 and 100 having respective openings 102 and 104. A pressure relief valve closure element 106 is mounted externally of plate 98 and is connected thereto by a number of springs 108 which normally retain closure 106 seated against plate 98 around opening 102 to prevent the escape of gases from tank 70 and shaft 82 as the effluent level fluctuates between limits 78 and 80 and as bag 92 correspondingly fuctuates between respective fully collapsed and fully inflated conditions.

As described with respect to FIG. 1, during each period of time required for the effluent to rise from level 78 to level 80, a small amount of excess gas is produced in tank 70 by bacterial action within the effluent. Since, when the effluent reaches upper limit 80, bag 72 will already be fully inflated due to the volumetric displacement of the gases between levels 78 and 80, the excess gas will cause valve element 106 to be unseated from plate 98 and will vent to the atmosphere through opening 102,.thereby maintaining the gases in the tank at substantially atmospheric pressure.

Valve element 106 will similarly vent gases from the tank when the effluent abnormally rises above upper limit 80, such as during heavy rain periods as previously described with respect to FIG. 1.

Valve 94 also includes a vacuum relief closure element 110 mounted internally of plates 100 and connected thereto by springs 112 which normally maintain closure 110 seated against plate 100 around opening 104. However, when a vacuum tends to be created in tank-70, e.g., upon a lowering of the abnormally high effluent level above limit 80 immediately after a heavy rain period, closure element 110 will be unseated from plate 100 to permit atmospheric air to enter the tank through opening 104, and thereby maintain the gases in the tank at atmospheric pressure.

In operation, when the effluent is at level 78, bag 92 is fully collapsed and will become fully inflated when the effluent rises to upper limit 80. When the level 80 is reached, the excess gas produced by bacterial action in the effluent will cause a rise in tank pressure above atmospheric and will effect venting through valve opening 102 until the pressure in the tank is returned to atmospheric pressure thereby preventing any damage to bag 92. Similarly, venting will occur when the effluent abnormally rises above upper limit 80.

Following such an abnormal rise in the effluent level, as the level again falls toward lower limit 78, bag 92 will become fully collapsed before limit 78 is reached and a vacuum will tend to be created in the tank. However, vacuum closure 110 will be unseated and atmospheric air will enter the tank through valve opening 104 to maintain the gases in the tank at atmospheric pressure.

FIG. 4 illustrates an embodiment of the invention similar to FIG. 3 in which the top of enclosed tank 120, however, is above ground level 72 but, because of space limitations due to the use and presence of submerged pump assemblies 122 inside the tank, the bag 92 is mounted externally of the tank on pipe section 88 which is directly connected to the top of the tank. Similarly pipe section 90 and relief valve 94 are connected to the top of the tank.

The embodiment of FIG. 4 operates identically to that of FIG. 3, the only difference being the use of submerged pump assemblies 122 inside the tank driven by motors 123 to remove the effluent therefrom, rather than an outlet conduit such as conduit 76 of FIG. 3, and its associated external pump equipment. Motors 123 are operated by a float controlled switch assembly 124, which responds to the fluctuating level of the effluent in tank 120.

It is understood that various modifications may be made in the several illustrated embodiments without departing from the scope of the invention. For example, in the preferred embodiment of FIG. 1, the breathing assembly 40 may be modified so that the internally positioned bag 52 is constructed without a flapper valve 61 similar to bag 92 and is connected to a pipe section 43 stationarily mounted through top wall 18 of tank 10. Tank 10 would'then be provided with a relief valve, such as valve 94, to maintain the gas pressure in the tank at atmospheric pressure.

It is apparent therefore, that the invention accomplishes the objects initially set forth by providing an inexpensive, relatively simply constructed sewage lift station which is capable of eliminating offensive odors from the atmosphere surrounding the lift station, while at the same time maintaining substantially atmospheric pressure conditions in the sewage tank to enhance effective effluent flow through the sewage system.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

l. A sewage lift station comprising a closed tank having an effluent inlet and an effluent outlet in the lower portion thereof, pump means connected to said outlet for pumping effluent from said tank, means responsive to the fluctuating effluent level in said tank for energizing said pump means when said effluent rises to a predetermined upper level and for deenergizing said pump means when said effluent drops to a predetermined lower level, a space in the upper portion of said tank in which sewer gas may collect, variable volume means connected to said tank and operative normally to isolate the interior thereof from the surrounding atmosphere, said variable volume means being responsive to the difference between atmospheric pressure and the gas pressure in said tank to maintain the gas pressure in said tank at substantially atmospheric pressure as the effluent level rises and falls between said predetermined upper and lower levels within said tank, whereby offensive odors from the interior of said tank and objectionable gaseous discharges are substantially eliminated from the atmosphere surrounding said tank.

2. A sewage lift station as defined in claim 1, and vent means for venting innocuous quantities of said sewer gas to the atmosphere when an excess of said gas accumulates over a period of time and when an abnormal rise in the effluent level in said tank occurs.

3. A sewage lift station as defined in claim 2, said variable volume means comprising a flexible bag positioned within said tank, the exterior of said bag subjected to the gas pressure in said tank while the interior thereof is subjected to the pressure of the surrounding atmosphere.

4. A sewage lift station as defined in claim 2, said variable volume means comprising a flexible bag positioned outside said tank, the interior of said bag being subjected to the gas pressure in said tank while the exterior thereof is subjected to the pressure of the surrounding atmosphere.

5. A sewage lift station as defined in claim 2, said vent means comprising pressure and vacuum relief valve means connected to said tank and operative to vent gases from said tank to the surrounding atmosphere when the gas pressure in said tank tends to increase above atmospheric pressure and to permit air from the atmosphere to enter said tank when a vacuum tends to be created therein.

6. A sewage lift station as defined in claim 2, wherein the maximum volume of said variable volume means corresponds substantially to the volume of gas in said tank displaced as said effluent fluctuates between said predetermined limits.

7. A sewage lift station comprising a closed tank having an effluent inlet and an effluent outlet in the lower portion thereof, pump means connected to said outlet for pumping effluent from said tank, means responsive to the fluctuating effluent level in said tank for energizing said pump means when said effluent rises to a predetermined upper level and for deenergizing said pump means when said level drops to a predetermined lower level, a space in the upper portion of said tank in which sewer gas may collect, and operative means connected tosaid tank operative normally to isolate the interior thereof from the surrounding atmosphere, thereby preventing egress of said sewer gas from the tank as the effluent level rises and falls between said predetermined upper and lower levels within said tank, and to vent innocuous quantities of said sewer gas to the atmosphere when an excess of said gas accumulates over a period ot time and when an abnormal rise in the effluent level in said tank occurs, said operative means comprising a breathing assembly including a fitting freely extending through a wall opening in said tank and having an annular flange at one end normally sealingly seated relative to said opening, and variable volume means connected to said fitting and being responsive to the gas pressure in said tank to maintain said gas pressure at substantially atmospheric pressure, whereby offensive odors from the interior of said tank and objectionable gaseous discharges are substantially eliminated from the atmosphere surrounding said tank.

8. A sewage lift station as defined in claim 7, said variable volume means comprising a flexible bag positioned within said tank, the interior of said bag being exposed to atmospheric pressure through said fitting and the exterior thereof being exposed to sewer gas pressure in said tank, said bag collapsing and expanding as the sewage level in said tank rises and falls to normally maintain the sewer gas pressure substantially equal to atmospheric pressure.

9. A sewage lift station as defined in claim 8, wherein the outer periphery of said fitting is spaced from the tank wall portion defining said wall opening to provide an annular passageway therebetween, said bag being suspended from said fitting and the'weight of said bag normally retaining said flange sealingly seated with said external wall surface around said opening, said breathing assembly being operative to unseat said flange and vent said sewer gas through said passage when said sewer gas pressure exceeds atmospheric pressure by a predetermined amount sufficient to substantially fully collapse said flexible bag and unseat said annular flange relative to said external wall surface.

10. A sewage lift station as defined in claim 8, wherein the maximum volumetric size of said bag corresponds substantially to the volume of gas in said tank displaced as said effluent level fluctuates between said limits.

I]. A breathing assembly for use in a sewage lift station which includes a closed tank comprising a tubular fitting adapted to extend through an opening in the tank in spaced relation with the wall portion of the tank defining the opening to form an annular passage therebetween and including a flange on one end thereof adapted to be sealingly seated outside the tank around the opening, a flexible bag connected to the other end of said fitting and adapted to be positioned within the tank, said bag being in open communication through said fitting with the atmosphere surrounding said tank so that said bag expands and contracts in response to the difference between atmospheric pressure and the pressure in said tank to thereby maintain the pressure in said tank at substantially atmospheric pressure, and said bag having means permitting the escape of gas from the interior thereof into the tank to prevent an excessive rupturing pressure differential between the inside and outside of the bag. 7

12. A breathing assembly for use in a sewage lift station as defined in claim 11, said bag adapted to correspond volumetrically in size to the volume of gas displaced in the tank by the fluctuation of sewage effluent between predetermined limits in the tank.

13. A sewage lift station comprising a tank having an effluent inlet and an effluent outlet in the lower portion thereof, a space in the upper portion thereof in which sewer gas may collect, a breathing assembly connected to said tank and operative normally to isolate the interior of said tank from the surrounding atmosphere and to maintain said sewer gas against egress from the tank as the effluent level rises and falls between predetermined levels within said tank, said breathing assembly including a fitting freely extending through a wall opening in said tank inspaced relation from the tank wall portion defining the opening to provide an annular passage therebetween, an annular flange at one end of said fitting normally sealingly seated. relative to said opening, a variable volume flexible bag connected to said fitting and positioned within said tank, the interior of said bag being exposed to atmospheric pressure through said fitting and the exterior thereof being exposed to sewer gas pressure in said tank, said bag collapsing and expanding as the effluent level in said tank rises and falls to normally maintain the sewer gas pressure within the tank substantially equal to atmospheric pressure, said flexible bag comprising means permitting the escape of the gas from the interior thereof into said space to prevent rupture of said bag due to excessive pressure internally thereof, and said breathing assembly being operative to vent sewer gas through said annular passage when said sewer gas pressure exceeds atmospheric pressure by a predetermined amount sufficient to substantially fully collapse said flexible bag and unseat said annular flange relative to said wall opening.

14. A breathing assembly for use in a sewage lift station which includes a closed tank in which sewage effluent collects and fluctuates in level between predetermined upper and lower levels, said assembly comprising tubular means adapted to extend through an opening in said tank, a flexible bag connected to one end of said tubular means and adapted to be positioned within the tank, said bag being in open communication through said tubular means with the atmosphere surrounding said tank so that said bag expands and contracts in response to the difference between atmospheric pressure and the pressure in said tank to thereby maintain the pressure in said tank at substantially atmospheric pressure, and said bag corresponding volumetrically in size to the volume of gas displaced in the tank by the fluctuation of the effluent in the tank between the predetermined upper and lower levels.

I UNITEb STATES PATENT OFFICE CERTIFICATE OF CORRECTION P n 3.807.901 Dated April 30 1974 Inventor(s) onal E. Wilson It is certified that-error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, lines 18 and 19, delete "not shown" and substitute -assembly 29(b) Column 4, line 64, after "additional" -insert --effluent--. Colunm 7, line 17, change "plates" to --plate-. 4

Figure 1 should be as shown on the attached sheet.

Signed and sealed this 13th day of May 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks 

1. A sewage lift station comprising a closed tank having an effluent inlet and an effluent outlet in the lower portion thereof, pump means connected to said outlet for pumping effluent from said tank, means responsive to the fluctuating effluent level in said tank for energizing said pump means when said effluent rises to a predetermined upper level and for deenergizing said pump means when said effluent drops to a predetermined lower level, a space in the upper portion of said tank in which sewer gas may collect, variable volume means connected to said tank and operative normally to isolate the interior thereof from the surrounding atmosphere, said variable volume means being responsive to the difference between atmospheric pressure and the gas pressure in said tank to maintain the gas pressure in said tank at substantially atmospheric pressure as the effluent level rises and falls between said predetermined upper and lower levels within said tank, whereby offensive odors from the interior of said tank and objectionable gaseous discharges are substantially eliminated from the atmosphere surrounding said tank.
 2. A sewage lift station as defined in claim 1, and vent means for venting innocuous quantities of said sewer gas to the atmosphere when an excess of said gas accumulates over a period of time and when an abnormal rise in the effluent level in said tank occurs.
 3. A sewage lift station as defined in claim 2, said variable volume means comprising a flexible bag positioned within said tank, the exterior of said bag subjected to the gas pressure in said tank while the interior thereof is subjected to the pressure of the surrounding atmosphEre.
 4. A sewage lift station as defined in claim 2, said variable volume means comprising a flexible bag positioned outside said tank, the interior of said bag being subjected to the gas pressure in said tank while the exterior thereof is subjected to the pressure of the surrounding atmosphere.
 5. A sewage lift station as defined in claim 2, said vent means comprising pressure and vacuum relief valve means connected to said tank and operative to vent gases from said tank to the surrounding atmosphere when the gas pressure in said tank tends to increase above atmospheric pressure and to permit air from the atmosphere to enter said tank when a vacuum tends to be created therein.
 6. A sewage lift station as defined in claim 2, wherein the maximum volume of said variable volume means corresponds substantially to the volume of gas in said tank displaced as said effluent fluctuates between said predetermined limits.
 7. A sewage lift station comprising a closed tank having an effluent inlet and an effluent outlet in the lower portion thereof, pump means connected to said outlet for pumping effluent from said tank, means responsive to the fluctuating effluent level in said tank for energizing said pump means when said effluent rises to a predetermined upper level and for deenergizing said pump means when said level drops to a predetermined lower level, a space in the upper portion of said tank in which sewer gas may collect, and operative means connected to said tank operative normally to isolate the interior thereof from the surrounding atmosphere, thereby preventing egress of said sewer gas from the tank as the effluent level rises and falls between said predetermined upper and lower levels within said tank, and to vent innocuous quantities of said sewer gas to the atmosphere when an excess of said gas accumulates over a period ot time and when an abnormal rise in the effluent level in said tank occurs, said operative means comprising a breathing assembly including a fitting freely extending through a wall opening in said tank and having an annular flange at one end normally sealingly seated relative to said opening, and variable volume means connected to said fitting and being responsive to the gas pressure in said tank to maintain said gas pressure at substantially atmospheric pressure, whereby offensive odors from the interior of said tank and objectionable gaseous discharges are substantially eliminated from the atmosphere surrounding said tank.
 8. A sewage lift station as defined in claim 7, said variable volume means comprising a flexible bag positioned within said tank, the interior of said bag being exposed to atmospheric pressure through said fitting and the exterior thereof being exposed to sewer gas pressure in said tank, said bag collapsing and expanding as the sewage level in said tank rises and falls to normally maintain the sewer gas pressure substantially equal to atmospheric pressure.
 9. A sewage lift station as defined in claim 8, wherein the outer periphery of said fitting is spaced from the tank wall portion defining said wall opening to provide an annular passageway therebetween, said bag being suspended from said fitting and the weight of said bag normally retaining said flange sealingly seated with said external wall surface around said opening, said breathing assembly being operative to unseat said flange and vent said sewer gas through said passage when said sewer gas pressure exceeds atmospheric pressure by a predetermined amount sufficient to substantially fully collapse said flexible bag and unseat said annular flange relative to said external wall surface.
 10. A sewage lift station as defined in claim 8, wherein the maximum volumetric size of said bag corresponds substantially to the volume of gas in said tank displaced as said effluent level fluctuates between said limits.
 11. A breathing assembly for use in a sewage lift station which includes a closed tank comprising a tubular fitting adapted to extend through an opening in the tank in spaced relation with the wall portion of the tank defining the opening to form an annular passage therebetween and including a flange on one end thereof adapted to be sealingly seated outside the tank around the opening, a flexible bag connected to the other end of said fitting and adapted to be positioned within the tank, said bag being in open communication through said fitting with the atmosphere surrounding said tank so that said bag expands and contracts in response to the difference between atmospheric pressure and the pressure in said tank to thereby maintain the pressure in said tank at substantially atmospheric pressure, and said bag having means permitting the escape of gas from the interior thereof into the tank to prevent an excessive rupturing pressure differential between the inside and outside of the bag.
 12. A breathing assembly for use in a sewage lift station as defined in claim 11, said bag adapted to correspond volumetrically in size to the volume of gas displaced in the tank by the fluctuation of sewage effluent between predetermined limits in the tank.
 13. A sewage lift station comprising a tank having an effluent inlet and an effluent outlet in the lower portion thereof, a space in the upper portion thereof in which sewer gas may collect, a breathing assembly connected to said tank and operative normally to isolate the interior of said tank from the surrounding atmosphere and to maintain said sewer gas against egress from the tank as the effluent level rises and falls between predetermined levels within said tank, said breathing assembly including a fitting freely extending through a wall opening in said tank in spaced relation from the tank wall portion defining the opening to provide an annular passage therebetween, an annular flange at one end of said fitting normally sealingly seated relative to said opening, a variable volume flexible bag connected to said fitting and positioned within said tank, the interior of said bag being exposed to atmospheric pressure through said fitting and the exterior thereof being exposed to sewer gas pressure in said tank, said bag collapsing and expanding as the effluent level in said tank rises and falls to normally maintain the sewer gas pressure within the tank substantially equal to atmospheric pressure, said flexible bag comprising means permitting the escape of the gas from the interior thereof into said space to prevent rupture of said bag due to excessive pressure internally thereof, and said breathing assembly being operative to vent sewer gas through said annular passage when said sewer gas pressure exceeds atmospheric pressure by a predetermined amount sufficient to substantially fully collapse said flexible bag and unseat said annular flange relative to said wall opening.
 14. A breathing assembly for use in a sewage lift station which includes a closed tank in which sewage effluent collects and fluctuates in level between predetermined upper and lower levels, said assembly comprising tubular means adapted to extend through an opening in said tank, a flexible bag connected to one end of said tubular means and adapted to be positioned within the tank, said bag being in open communication through said tubular means with the atmosphere surrounding said tank so that said bag expands and contracts in response to the difference between atmospheric pressure and the pressure in said tank to thereby maintain the pressure in said tank at substantially atmospheric pressure, and said bag corresponding volumetrically in size to the volume of gas displaced in the tank by the fluctuation of the effluent in the tank between the predetermined upper and lower levels. 